Topic 8: Photosynthesis- BIO 1020

What is photosynthesis?

conversion of solar energy into chemical energy

what is an autophototroph

produce organic molecules from CO2 and other inorganic materials

what is a photoautotroph

autotrophs that use light as a source of energy

what are heterotrophs

obtain organic material by consuming it, they’re consumers of the biosphere

where does photosynthesis take place?

enzymes and other necessary molecules are grouped together in biological membranes. Takes place in chloroplasts in eukaryotic organisms

what is the main location of chloroplasts?

mesophyll cells. which is the tissue in the interior of the leaf

how many chloroplasts are there per cell?

30-40

what is the stomata (stoma)?

Pores in a leaf that allow the entry of CO2 and the exit of O2. they open and close allowing the movement of CO2 and O2

what is the function of veins?

deliver water and sugars to all parts of the plant (top to bottom)

what is the chloroplasts structure?

double membrane

stroma

fluid inside the inner chloroplast membrane

thylakoids

sacs of membrane suspended in the storm

thylakoid space

space inside the thylakoids

grana (granum)

stacks of thylakoids

chlorophyll

pigment molecule that absorbs light energy and is embedded in the thylakoids

what is the chemical reaction for photosynthesis

6CO2 + 6H20 + light energy = C6H12O6 + 6O2 , (opposite of cellular respiration)

what molecules in photosynthesis are being reduced and oxidized?

CO2 is reduced, while H2O is oxidized

electrons increase in potential when..

they move from water to sugar

photosynthesis is what kind of reaction?

endergonic since it consumes energy from the light and redox

what are the two stages of photosynthesis?

The light reactions and the Calvin cycle

what happens in the light reactions stage of photosynthesis?

conversion of solar energy to chemical energy

what the the Calvin cycle?

conversion of CO2 to organic molecules, reducing carbon into carbohydrates

photophosphorylation

when chemiosmosis adds a phosphate group to ADP

wavelength

the distance between the crests of electromagnetic waves

electromagnetic spectrum

full range of radiation

photon

discrete particles of light. packets of light energy

the shorter the wavelength..

the great the energy of each photon

pigments

substances that absorb visible light

the colour we see is…

the wavelength of light that is reflected or transmitted

spectrophotometer

instrument that measures the ability of a pigment to absorb various wavelengths of light

absorption spectrum

graph plotting the pigments light absorption versus wavelength

chlorophyll a

Key light capturing a pigment. Participates directly in light reactions

Chlorophyll b

Accessory pigment, works in conjunction with chlorophyll a. Unstable pigment so breaks down easier

Carotenoids

Accessory light harvesting pigments

what do carotenoids do?

protect the cells from damage due to excessive light energy

when a molecule absorbs a photon…

one of the molecules electrons is elevated to an orbital where t has more potential energy.

A photons energy matches…

the difference between the ground state and the excited state

ground state

electron is in its normal orbital

excited state

electron in an orbital of higher energy

what happens when an electron drops down an energy level?

it releases heat and energy

reaction centre (RC)

proteins holding a special pair of chlorophyll a molecules

Light harvesting complex (LHC)

pigment molecules bound to proteins

Primary electron acceptor

molecule capable of accepting electrons from the RC chlorophyll a molecules

how many photosystems cooperate in light reactions?

2

which photosystem functions first?

Photosystem II. RC chlorophyll a is known as P680

which photo system functions second?

Photosystem I. RC chlorophyll is P700

describe the cyclic electron flow

uses photosystems I without using II. Electron cycle back from ferredoxin (transport chain molecule), to the cytochrome complex and then to a P700 chlorophyll. No NADH or O2. ATP is produced

photosynthetic bacteria have one photosystem meaning…

they are probably descendants of ancestral bacteria in which photosynthesis first evolved

Cyanobacteria and plants have both photosystems meaning…

they can carry out cyclic electron flow in certain conditions. They can switch back and forth

what does it mean for a plant if they dont use cyclic electron Flow?

they can grow well in low light but not intense light, meaning cyclic electron Flow may be photo protective

chemiosmosis

ATP synthase couples the diffusion of hydrogen ions down their gradient for the phosphorylation of ADP to form ATP

in chemiosmosis, where do the H ions diffuse to?

from the thylakoid space to the stroma

what structures carry out chemiosmosis?

the mitochondria and chloroplast

describe the Calvin Cycle

cyclic cycle that uses chemical energy of ATP and the electrons carried by NADPH to reduce CO2 to sugar

what type of pathway is the Calvin cycle

anabolic. it builds carbohydrates from smaller molecules and consuming energy

what does the Calvin cycle produce?

Glyceralhyde-3-phosphate (G3P). 3 carbon sugar, the cycle turns 3 times to make one G3P. Each turn of the cycle fixes one molecule of CO2

describe the first step of the carbon cycle

carbon fixation: incorporation of CO2 b attaching it to ribulose diphosphate (RuBP). it forms an unstable 6-carbon molecule that immediately breaks into two 3-carbon molecules; 3 phosphoglycerate

describe the second step of the Calvin cycle

reduction: electrons from NADPH reduces 3-phosphoglycerate to glyceraldehyde 3-phosphate (G3P). For every three turns of the cycle, 6 G3P are formed

in the second step of the Calvin cycle what is the net gain?

when 6 G3P are formed, only on is counted as net gain, the other five are required to complete the cycle

describe the third step of the Calvin cycle

regeneration of RuBP: 5 molecules of G3P are rearranged into three molecules of RuBP, with an input of 3 ATP

what are the inputs and outputs of the Calvin cycle

input: 9 ATP, 6 NADPH, and 3 CO2 output: 1 glyceraldehyde, 3-phosphate which can be used to synthesize other organic compounds such as glucose

what type of property is photosynthesis and what does the entail?

its an emergent property, which integrates the light and dark reactions to make sugars from inorganic carbon

what enzyme is most important for the Calvin cycle?

ribulose biphosphate (RuBP)

what are the reactants and products of the Calvin cycle?

reactants: CO2, ATP, NADPH, RuBP products:G3P, ADO, NADP+, inorganic phosphate

what electron carriers are used in the Calvin cycle?

NADPH